Abstract: An electronic flash unit has a flash tube and a flash circuit which includes an internal light sensor that interrupts the supply of electricity to the flash tube when it senses that the flash light reflected from an object exceeds a predetermined threshold value. The unit also has a connector for connecting it to an external light sensor and an arrangement for disconnecting the internal sensor from the circuit when connection is made to an external sensor, and vice versa. An adapter circuit is connected to the connector and allows the unit to be used with a camera having its own built-in light sensor so that, when the unit is used with such a camera, the camera sensor performs the function otherwise performed by the internal sensor of the unit.

Abstract: The flash unit includes a flash element and a first electronic switch connected in the current path of the flash element. The flash element is ignited by rendering the first switch conductive. Flash-terminating circuitry terminates the flash by rendering the first switch non-conductive. The flash-terminating circuit includes a commutation capacitor and a second electronic switch interconnected with each other and with the first switch for applying the commutation capacitor voltage to the first electronic switch as a reverse-bias voltage when the second electronic switch is rendered conductive. The second electronic switch is a two-electrode electronic switch which can be rendered conductive by raising the voltage across its electrodes above the value at which such voltage is normally maintained.

Abstract: The circuit includes voltage supply terminals for connection to a voltage source and battery connection terminals for connection to a battery to be charged. Circuitry connects the voltage supply terminals to the battery connection terminals for the transmission of a charging voltage and provides a current path for the flow of charging current. A controllable switch is connected to the charging current path and has conductive and non-conductive states. A second controllable switch is connected to the first controllable switch and is operative upon the receipt of a control signal having a predetermined threshold value for changing the state of the first controllable switch. The second controllable switch receives a control signal whose value varies in dependence upon variations in the charging current and/or the charging voltage. Circuitry is provided for changing the threshold value of the second controllable switch in automatic dependence upon changes in the charging current and/or the charging voltage.

Abstract: A chopper circuit arrangement for charging an electronic flash discharge capacitor and for turning off the chopper is disclosed. The arrangement operates from a D.C. source and includes chopper transistors and a transformer operating together as a converter. Regenerative means, including a feedback winding of the transformer, function to charge the flash discharge capacitor. The arrangement includes transistors disposed across the chopper transistors to block or hold the converter off. These blocking transistors are activated when the voltage across the discharge capacitor has achieved a predetermined value. The arrangement includes means for effectuating blocking of the converter only during the off condition of the chopper. The arrangement also includes means for delaying the charge of the discharge capacitor, after discharge, for a predetermined time.

Abstract: A circuit arrangement for charging a flash capacitor of a designated rated voltage from a DC source of a higher rated voltage. A thyristor in the line from the DC source is blocked when the voltage for which the flash capacitor is designed is reached.

Abstract: A circuit for igniting an electronic flashtube including a thyristor connected in series with the flashtube and an ignition capacitor connected through a switching thyristor to an ignition transformer to trigger the flashtube. The state of the series thyristor is controlled by means such as an electronic threshold switch to provide proper switching operation over a range of flashtubes with different specimen variations with respect to the time required to build up plasma.